1. Field of the Invention
The present invention relates generally to network restoration, and more specifically the present invention is directed toward distributed network restoration using prioritized restoration signals.
2. Related Art
A telecommunications network comprises a plurality of nodes connected together by logical spans that may comprise links of optical fibers. If any of the fibers are cut, the traffic through a portion of the network is disrupted. In conventional solutions, automatic protection switching (e.g., 1:1 or 1:N) moves disrupted traffic to dedicated spare circuits promptly, typically in less than 50 milliseconds. However, this automatic protection switching requires a high dedicated spare channel capacity.
Similarly, self-healing rings (e.g., unidirectional or bidirectional) suffer from the same problem of high dedicated spare channel capacity. In this network solution, a common protection ring is shared by all of the nodes on the ring. Although switching times are attractive in ranging from 50-200 milliseconds, self-healing rings prove inflexible when considering provisioning, growth and maintenance issues. Moreover, self-healing rings are limited in their response to multiple failure scenarios.
Digital cross connect mesh architectures, on the other hand, provide the maximum flexibility in responding to network failures. In these systems, each node contains one or more digital cross connect systems that connect via logical spans to a plurality of other nodes in a mesh-like configuration. The spare capacities in each of the logical spans contributes to the survivability of other spans in the network.
There are two distinct types of digital cross connect mesh architectures: centralized and distributed. In a centralized mesh architecture, a centralized intelligence has a built in knowledge of the different nodes and links of the network and a defined solution for a particular failure scenario. A disadvantage of this scheme is that the topology of the network has to be stored in a centralized database that requires updating any time a network change occurs (e.g., addition or removal of links). Additionally, the restoration time is typically on the order of minutes.
In a distributed mesh architecture, the intelligence is distributed in each of the nodes of the network. This intelligence is created through a variety of signaling messages that are passed between adjacent nodes. Currently, there are two types of distributed restoration schemes: span (or link) based and path based. In path based schemes, the shortest and/or most reasonable end-to-end alternate route throughout the network is found.
In link based schemes, on the other hand, the shortest and/or most reasonable alternate route is identified between the nodes adjacent to the failed link. One example of a conventional link based solution is described in U.S. Pat. No. 4,956,835 to Grover which is herein incorporated by reference in its entirety. This technique is commonly referred to as "Selfhealing Networks".TM. or "SHN." SHN is a protocol consisting of restoration-specific data structures that are communicated through the network, operating logic within each network node, and a defined sequence of network events to accomplish restoration.
Generally, Grover's SHN algorithm is directed to the restoration of a failure in a single logical span. If failures in multiple logical spans exist, multiple sender-chooser pairs compete for a finite set of spare resources. An efficient distributed restoration algorithm must therefore provide a mechanism for solving this resource contention problem.